1. The Field of the Invention
The present invention relates generally to packaging devices. More particularly, exemplary embodiments of the present invention concern packaging for optoelectronic components and devices, where such packaging isolates the components and devices from the effects of applied forces.
2. Related Technology
Fiber optic technology is frequently employed in computer and computer networking applications. Fiber optic lines or cables are often used to interconnect computers and computer networks. Generally speaking, computer networks configured using fiber optic cables offer improved bandwidth over conventional electronic networks. Therefore, development of technologies involving the use of fiber optic cables is increasing.
One area in which fiber optic technology is advancing relates to increasing the capacity of fiber optic networks while at the same time reducing cost. For example, wavelength division multiplexing (WDM) and dense wavelength division multiplexing (DWDM) technologies attempt to increase capacity and reduce cost by transmitting multiple optical signals through a single fiber wherein each signal is transmitted on a different optical wavelength or channel. Such a configuration requires that multiple optical signals be multiplexed for transmission and then demultiplexed to recover the individual signals, with the multiplexing and demultiplexing typically accomplished through the use of multiple thin-film optical filters.
The number of channels available for transmitting optical signals is a function of the channel spacing. Fiber optic capacity increases with more closely spaced channels. Channel spacing, however, is limited by the ability of the optical filters to resolve the channels. One way to minimize channel spacing is through the use of an interleaver, which combines two sets of channels into one densely packed set with half the channel spacing of the original sets, and a deinterleaver, which separates a plurality of optical channels into odd and even channels with a spacing twice as large as the spacing of the original channels. Therefore, use of an interleaver in combination with a multiplexer allows for much smaller channel spacing than does a multiplexer alone.
While useful, multiplexers and interleavers are generally configured using a large number of optical components. Such components may include beam splitters, half-wave plates, quarter-wave plates, reflectors, prisms, beam displacers, lenses, and the like. For an interleaver to function properly, each constituent component must be carefully aligned with respect to the other components. Such alignment is typically achieved by mounting each component to a planar reference structure, such as a stage, box, or frame.
Not only are the components of multiplexers or interleavers carefully aligned, the components are often placed inside a hermetically sealed package. By hermetically sealing the optical components in this way, contaminants, such as moisture, that would have a deleterious effect on the device, are kept away from the optical components.
A hermetically sealed package is typically made by seam sealing one or more lids onto a box or frame after the optical components have been placed in their proper positions. Common techniques for seam sealing include welding and gluing. Laser welding is particularly common for fiber-optic device packaging.
While hermetically sealing an optical device package is beneficial in protecting optical components, sealing a package without disturbing the alignment of the components within the package is difficult. The sealing process can generate a significant amount of heat, causing thermal distortion of parts, or can create mechanical stress from solidification contraction forces.
Problems involving protecting optical components while sealing an optical package have been addressed in the past by careful analysis and characterization of the sealing process, such that the shifts in alignment of the optical components are well-understood and replicable. The information concerning the shifts in alignment of the optical components is used to develop methods for compensating for the misalignment, such as assembling the optical components out of alignment and then bringing the optical components into alignment by the sealing process. In the case of laser welding, the predictability of the alignment shifts can be enhanced by careful selection of beam-delivery optics, weld schedule, and the use of simultaneous multiple welds. Still, the alignment accuracy offered by such techniques is not satisfactory for many applications. In addition, the effort needed to analyze the sealing process for a particular product can be both expensive and time-consuming.
Moreover, packaged optical devices are typically mounted onto another structure when used for their intended purpose. The packaged optical devices may be attached in various conventional ways, such as with screws or with epoxy. Mounting the package is another source of forces which can result in the creation of mechanical stress on the package that may disturb the alignment of the optical components in the package. Further, effects such as mechanical stress may arise because of forces that result from differing thermal characteristics, such as the coefficient of thermal expansion, of the materials of the package and the mounting structure. Thus, it is nearly impossible to characterize and compensate for all effects related to forces associated with the mounting of optical devices or other devices.
Therefore, what is needed is a package that is relatively insensitive to effects, such as mechanical and thermal stresses, that can result from the application of forces to the package, so that the components in the package substantially maintain their respective alignments even through the sealing process. Such a package would offer high performance and high reliability, but at a substantially lower cost.